1. Field of the Invention
The present invention relates to an optical biological information detecting apparatus and an optical biological information detecting method that can optically detect biological information.
2. Description of the Related Art
As described in Japanese Patent Application KOKAI Publication No. 2001-353133, an optical biological information detecting apparatus combined with a wristwatch has been known.
An optical biological information detecting apparatus of a wristwatch type comprises a light emitting unit that emits observation light having a predetermined wavelength and a light receiving unit that receives scattered light of the observation light emitted from the light emitting unit and scattered in a biological tissue, which are provided on a back cover of the wristwatch. The optical biological information detecting apparatus causes the light emitting unit to intermittently emit light for a constant time with a constant period, causes the light receiving unit to receive the scattered light from the biological tissue according to pulsative light emission of the light emitting unit, performs photoelectric conversion, performs a frequency analysis on signals obtained by continuous observation for a predetermined time, and estimates biological information, such as a pulse wave.
The outline of an operational principle of the biological information detecting apparatus is as described above. However, according to the operational principle, absorbance where hemoglobin of blood absorbs light greatly changes at about 600 nanometers (hereinafter, simply referred to as nm), and the absorbance is very high at a wavelength shorter than 600 nm, as compared with a wavelength of 600 nm or more. For this reason, light having the wavelength shorter than 600 nm is generally used as the observation light emitted from the light emitting unit.
However, the biological information detecting apparatus according to the related art uses dermis including a blood capillary in a surface of a skin and epidermis containing melanine pigment of the surface side as an observation object of a pulse wave. However, if a large amount of melanine pigment is contained in the epidermis, the observation light may be absorbed by the melanine pigment. As a result, biological information, such as a pulse wave, cannot be accurately detected.
That is, the melanine pigment has extraordinarily high absorbance in a wavelength band from ultraviolet light to visible light. When the large amount of melanine pigment is contained in the epidermis (for example, in the case of a person of a dark skin color), even though observation light having a wavelength of 600 nm or less is irradiated onto the skin, the observation light that reaches the dermis including the blood capillary, repeats scattering and absorption in a dermis tissue, passes through the epidermis again, and arrives at the light receiving unit is weak light and cannot be sufficiently received. Therefore, biological information, such as a pulse wave, cannot be detected.
The biological information detecting apparatus according to the related art is configured such that the light emitting unit and the light receiving unit are two-dimensionally disposed on an observation light taking plate, light emitted from the light emitting unit is irradiated onto the skin through the observation light taking plate facing the surface of the skin, scattered light thereof is taken by the observation light taking plate, and the scattered light is received by the light receiving unit through the observation light taking plate. When the light emitted from the light emitting unit is incident in the skin from the observation light taking plate, a portion of the light may be reflected on an inner surface of the observation light taking plate, and the light reflected on the inner surface of the observation light taking plate may be received by the light receiving unit as light noise. As a result, only the scattered light from the skin cannot be accurately detected.